L-aminodicarboxylic acid amides

ABSTRACT

Amides of α-aminodicarboxylic acids and β-aminoethers are low calorie sweetners.

This application is a continuation-in-part of copending U.S. patent application Ser. No. 686,570 filed Dec. 27, 1984.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel group of compounds and more particularly to a novel group of compounds particularly well suited as sweeteners in edible foodstuff.

2. Description of the Prior Art

Sweetness is one of the primary taste cravings of both animals and humans. Thus, the utilization of sweetening agents in foods in order to satisfy this sensory desire is well established.

Naturally occuring carbohydrate sweeteners such as sucrose, are still the most widely used sweetening agents. While thse naturally occurring carbohydrates, i.e., sugars, generally fulfill the requirements of sweet taste, the abundant usage thereof does not occur without deleterious consequence, e.g., high caloric intake and nutritional imbalance. In fact, oftentimes the level of these sweeteners required in foodstuffs is far greater than the level of the sweetener that is desired for economic, dietetic or other functional consideration.

In an attempt to eliminate the disadvantages concomitant with natural sweeteners, considerable research and expense have been devoted to the production of artificial sweeteners, such as for example, saccharin, cyclamate, dihydrochalcone, aspartame, etc. While some of these artificial sweeteners satisfy the requirements of sweet taste without caloric input, and have met with considerable commercial success, they are not, however, without their own inherent disadvantages. For example, many of these artificial sweeteners have the disadvantages of high cost, as well as delay in the perception of the sweet taste, persistent lingering of the sweet taste, and very objectionable bitter, metallic aftertaste when used in food products.

Since it is believed that many disadvantages of artificial sweeteners, particularly aftertaste, is a function of the concentration of the sweetener, it has been previously suggested that these effects could be reduced or eliminated by combining artificial sweeteners such as saccharin, with other ingredients such as aspartame or natural sugars, such as sorbitol, dextrose, maltose, etc. These combined products, however, have not been entirely satisfactory either. Some U.S. patents which disclose sweetener mixtures include for example, U.S. Pat. No. 4,228,198; U.S. Pat. No. 4,158,068; U.S. Pat. No. 4,154,862; and U.S. Pat. No. 3,717,477.

Accordingly, much work has continued in an attempt to develop and identify compounds that have a sweet taste and which will satisfy the need for better lower calorie sweeteners. Search continues for sweeteners that have intense sweetness, that is, deliver a sweet taste at low use levels and which will also produce enough sweetness at low levels to act as sole sweetener for most sweetener applications. Furthermore, the sweeteners sought must have good temporal and sensory qualities. Sweeteners with good temporal qualities produce a time-intensity sweetness response similar to natural sweeteners without lingering. Sweeteners with good sensory qualities lack undesirable off tastes and aftertaste. Furthermore, these compounds must be economical and safe to use.

In U.S. Pat. No. 3,798,204, L-aspartyl-O-t-butyl-L-serine methyl ester and L-aspartyl-O-t-amyl-L-serine methyl ester are described as sweet compounds having significant sweetness.

In U.S. Pat. No. 4,448,716 metal complex salts of dipeptide sweetners are disclosed. In the background of this patent a generic formula is described as an attempt to represent dipeptide sweeteners disclosed in five prior patents: U.S. Pat. No. 3,475,403; U.S. Pat. No. 3,492,131; Republic of South Africa Pat. No. 695,083 published July 10, 1969; Republic of South Africa Pat. No. 695,910 published Aug. 14, 1969; and German Pat. No. 2,054,554. The general formula attempting to represent these patents is as follows: ##STR1## wherein R represents the lower alkyls, lower alkylaryls and cycloalkyls, n stands for integers 0 through 5, R₁ represents (a) phenyl group, (b) lower alkyls, (c) cycloalkyls, (d) R₂.

Where R₂ is hydroxy, lower alkoxy, lower alkyl, halogen, (e) (S(O)_(m) (lower alkyl) where m is 0, 1 or 2 and provided n is 1 or 2, (f) R₃.

Where R₃ represents an hydroxy or alkoxy and (g) single or double unsaturated cycloalkyls with up to eight carbons. These compounds also are not entirely satisfactory in producing a high quality sweetness or in producing a sweet response at lower levels of sweetener.

Dipeptides of aspartyl-cysteine and aspartylmethionine methyl esters are disclosed by Brussel, Peer and Van der Heijden in Chemical Senses and Flavour, 4, 141-152 (1979) and in Z. Levensm. Untersuch-Forsch., 159, 337-343 (1975). The authors disclose the following dipeptides:

α-L-Asp-L-Cys(Me)-OMe

α-L-Asp-L-Cys(Et)-OMe

α-L-Asp-L-Cys(Pr)-OMe

α-L-Asp-L-Cys(i-Pr)-OMe

α-L-Asp-L-Cys(t-But)-OMe

α-L-Asp-L-Met-OMe

In U.S. Pat. No. 4,399,163 to Brennan et al., sweeteners having the following formulas are disclosed: ##STR2## and physiologically acceptable cationic and acid addition salts thereof wherein

R^(a) is CH₂ OH or CH₂ OCH₃ ;

R is a branched member selected from the group consisting of fenchyl, diisopropylcarbinyl, d-methyl-t-butylcarbinyl, d-ethyl-t-butyl-carbinyl, 2-methylthio-2,4-dimethylpentan-3-yl, di-t-butyl-carbinyl, ##STR3##

European Patent Application No. 34,876 describes amides of L-aspartyl-D-amino acid dipeptides of the formula: ##STR4## wherein R^(a) is methyl, ethyl, n-propyl or isopropyl and R is a branched aliphatic, alicyclic or heterocyclic member which is branched at the alpha carbon atom and also branched again at one or both of the beta carbon atoms. These compounds are indicated to be of signficant sweetness.

In the Journal of Medicinal Chemistry, 1984, Vol. 27, No. 12, pp. 1663-1668, are described various sweetener dipeptide esters, including L-aspartyl-α-aminocycloalkane methyl esters.

The various dipeptide esters of the prior art have been characterized as lacking significant stability at low pH values and/or thermal stability. These characterstics have limited the scope of use of these sweeteners in food products which are of low pH values or are prepared or served at elevated temperatures.

Accordingly, it is desired to find compounds that provide quality sweetness when added to foodstuffs or pharmaceuticals at low levels and thus eliminate or greatly diminish the aforesaid disadvantages associated with prior art sweeteners.

SUMMARY OF THE INVENTION

The present new compounds are amides of certain α-aminodicarboxylic acids and β-aminoethers which are low calorie sweeteners that possess a high order of sweetness with pleasing taste and higher stability at acid pH and elevated temperatures compared to known dipeptide sweeteners.

This invention provides new sweetening compounds represented by the formula: ##STR5## wherein A is hydrogen, alkyl containing 1-3 carbon atoms, hydroxyalkyl containing 1-3 carbon atoms or alkoxymethyl wherein the alkoxy contains 1-3 carbon atoms;

A' is hydrogen or alkyl containing 1-3 carbon atoms; alternatively

A and A' taken together with the carbon atom to which they are attached form cycloalkyl containing 3-4 carbon atoms;

Y is --(CHR₂)_(n) --R₁ or --CHR₃ R₄ ;

R₁ is cycloalkyl, cycloalkenyl, lower alkyl substituted cycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl or tricycloalkyl containing up to 10 ring carbon atoms and up to a total of 12 carbon atoms;

R₂ and R₅ are each H or alkyl containing 1-4 carbon atoms;

R₃ and R₄ are each cycloalkyl containing 3-4 ring carbon atoms;

n=0 or 1; and

m=0 or 1;

and food-acceptable salts thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, the preferred compounds are those in which R₁ is an alkyl-substituted cycloalkyl or bicycloalkyl containing 5-7 ring carbon atoms and up to a total of 10 carbon atoms. Especially preferred are cycloalkyl substituted with at least one methyl group on the β and/or β' carbon atoms of the cycloalkyl ring. Particularly preferred cycloalkyls include cyclopropyl, cyclopentyl, and cyclohexyl and the preferred bicycloalkyl is fenchyl.

Also preferred are those compounds in which R₅ =H and n=0. In those compounds in which n=1, R₁ is preferably a cyclopropyl group and R₂ is preferably tertiary butyl or isopropyl.

The ether groups representative of Y in the present new compounds include such groups as cycloalkyl, e.g., cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, etc.; alkyl-substituted cycloalkyls, e.g., 1-methylcyclopentyl, 1-methylcyclohexyl, 1-methylcyclobutyl, 1-methylcycloheptyl, 1-ethylcyclobutyl, 1-ethylcyclopentyl, 1-ethylcycloheptyl, 1-ethylcyclohexyl, 1-isopropylcyclobutyl, 1-isopropylcyclopentyl, 1-isopropylcyclohexyl, 1-isopropylcycloheptyl, 1,2-dimethylcyclohexyl, 1,2-dimethylcyclopentyl, 1,2-dimethylcycloheptyl, 1,3-dimethylcyclohexyl, 1,3-dimethylcyclopentyl, 1,3-dimethylcycloheptyl, 1,4-dimethylcyclohexyl, 1,4-dimethylcycloheptyl, 2,3-dimethylcyclopentyl, 2,3-dimethylcyclohexyl, 2,3-dimethylcycloheptyl, 2,4-dimethylcyclopentyl, 2,4-dimethylcyclohexyl, 2,4-dimethylcycloheptyl, 2,5-dimethylcyclopentyl, 2,5-dimethylcyclohexyl, 2,5-dimethylcycloheptyl, 2,6-dimethylcyclohexyl, 2,6-dimethylcycloheptyl, 2,7-dimethylcycloheptyl, 3,4-dimethylcyclopentyl, 3,4-dimethylcyclohexyl, 3,4-dimethylcycloheptyl, 3,5-dimethylcyclopentyl, 3,5-dimethylcyclohexyl, 3,5-dimethylcycloheptyl, 4,5-dimethylcyclopentyl, 4,5-dimethylcyclohexyl, 4,5-dimethylcycloheptyl, 3,6-dimethylcyclohexyl, 3,6-dimethylcycloheptyl, 3,7-dimethylcycloheptyl, 4,6-dimethylcycloheptyl, 4,6-dimethylcyclohexyl, 4,7-dimethylcycloheptyl, 5,6-dimethylcyclohexyl, 5,6-dimethylcyclohexyl, 5,6-dimethylcycloheptyl, 5,7-dimethylcycloheptyl, 6,7-dimethylcycloheptyl, 2,2-dimethylcyclopentyl, 2,2-dimethylcyclohexyl, 2,2-dimethylcycloheptyl, 3,3-dimethylcyclopentyl, 3,3-dimethylcyclohexyl, 3,3-dimethylcycloheptyl, 4,4-dimethylcyclohexyl, 4,4-dimethylcycloheptyl, 2,2,3-trimethylcyclopentyl, 2,2,3-trimethylcyclohexyl, 2,2,3-trimethylcycloheptyl, 2,2,4-trimethylcyclopentyl, 2,2,4-trimethylcyclohexyl, 2,2,4-trimethylcycloheptyl, 2,2,5-trimethylcyclopentyl, 2,2,5-trimethylcyclohexyl, 2,2,5-trimethylcycloheptyl, 2,2,6-trimethylcyclohexyl, 2,2,6-trimethylcyclohepty, 2,2,7-trimethylcycloheptyl, 1,2,2-trimethylcyclopentyl, 1,2,2-trimethylcyclohexyl, 1,2,2-trimethylcycloheptyl, 1,3,3-trimethylcyclopentyl, 1,3,3-trimethylcyclohexyl, 1,3,3-trimethylcycloheptyl, 1,4,4-trimethylcyclohexyl, 1,4,4-trimethylcyclopentyl, 3,3,4-trimethylcyclopentyl, 3,3,4-trimethylcyclohexyl, 3,3,4-trimethylcycloheptyl, 2,3,3-trimethylcyclopentyl, 2,3,3-trimethylcyclohexyl, 2,3,3-trimethylcycloheptyl, 2,4,4-trimethylcyclopentyl, 2,4,4-trimethylcyclohexyl, 2,4,4-trimethylcycloheptyl, 1,2,3-trimethylcyclopentyl, 1,2,3-trimethylcyclohexyl, 1,2,3-trimethylcycloheptyl, 1,2,4-trimethylcyclopentyl, 1,2,4-trimethylcyclohexyl, 1,2,4-trimethylcycloheptyl, 1,2,5-trimethylcyclopentyl, 1,2,5-trimethylcyclohexyl, 1,2,5-trimethylcycloheptyl, 1,2,6-trimethylcyclohexyl, 1,2,6-trimethylcycloheptyl, 1,2,7-trimethylcycloheptyl, 2,3,4-trimethylcyclopentyl, 2,3,4-trimethylcyclohexyl, 2,3,4-trimethylcycloheptyl, 2,3,5-trimethylcyclopentyl, 2,3,5-trimethylcyclohexyl, 2,3,5-trimethylcycloheptyl, 2,3,6-trimethylcyclohexyl, 2,3,6-trimethylcycloheptyl, 2,3,7-trimethylcycloheptyl, 3,4,4-trimethylcyclohexyl, 3,4,4-trimethylcyclopentyl, 2,2,5,5-tetramethylcyclopentyl, 2,2,5,5-tetramethylcyclohexyl, 2,2,5,5-tetramethylcycloheptyl, 2,2,6,6-tetramethylcyclohexyl, 2,2,6,6-tetramethylcycloheptyl, 2,2,7,7-tetramethylcycloheptyl, 2,2,4,4-tetramethylcyclopentyl, 2,2,4,4-tetramethylcyclohexyl, 2,2,4,4-tetramethylcycloheptyl, 2,2,3,3-tetramethylcyclopentyl, 2,2,3,3-tetramethylcyclohexyl, 2,2,3,3-tetramethylcycloheptyl, 3,3,4,4-tetramethylcyclopentyl, 3,3,4,4-tetramethylcyclohexyl, 3,3,4,4-tetramethylcycloheptyl, 3,3,5,5-tetramethylcyclohexyl, 3,3,5,5-tetramethylcycloheptyl, 1,2,3,4-tetramethylcyclopentyl, 1,2,3,4-tetramethylcyclohexyl, 1,2,3,4-tetramethylcycloheptyl, 1,2,3,5-tetramethylcyclopentyl, 1,2,3,5-tetramethylcyclohexyl, 1,2,3,5-tetramethylcycloheptyl, 1,2,3,6-tetramethylcyclohexyl, 1,2,3,6-tetramethylcycloheptyl, 2,3,4,5-tetramethylcyclopentyl, 2,3,4,5-tetramethylcyclohexyl, 2,3,4,5-tetramethylcycloheptyl, 2,3,4,6-tetramethylcycloheptyl, 2,3,4,6-tetramethylcyclohexyl, 2,3,4,7-tetramethylcycloheptyl, 2,2,3,4-tetramethylcyclopentyl, 2,2,3,4-tetramethylcyclohexyl, 2,2,3,4-tetramethylcycloheptyl, 2,2,3,5-tetramethylcyclopentyl, 2,2,3,5-tetramethylcyclohexyl, 2,2,3,5-tetramethylcycloheptyl, 2,2,3,6-tetramethylcyclohexyl, 2,2,3,6-tetramethylcycloheptyl, 2,2,3,7-tetramethylcycloheptyl, 2,3,3,4-tetramethylcyclohexyl, 2,3,3,4-tetramethylcyclopentyl, 2,3,3,4-tetramethylcycloheptyl, 2,3,3,5-tetramethylcyclopentyl, 2,2,3,5-tetramethylcyclohexyl, 2,3,3,5-tetramethylcycloheptyl, 2,3,3,6-tetramethylcyclohexyl, 2,3,3,6-tetramethylcycloheptyl, 2,3,3,7-tetramethylcycloheptyl, 2,2,3,4-tetramethylcyclopentyl, 2,2,3,4-tetramethylcyclohexyl, 2,3,3,4-tetramethylcycloheptyl, 2,2,3,5-tetramethylcyclopentyl, 2,2,3,5-tetramethylcyclohexyl, 2,2,3,6-tetramethylcyclohexyl, 2,2,3,6-tetramethylcycloheptyl, 2,2,3,7-tetramethylcycloheptyl, 2,2,4,5-tetramethylcyclopentyl, 2,2,4,5-tetramethylcyclohexyl, 2,2,4,5-tetramethylcycloheptyl, 2,2,4,6-tetramethylcyclohexyl, 2,2,4,6-tetramethylcycloheptyl, 2,2,4,7-tetramethylcycloheptyl, 4-methylcyclohexylisopropyl, 4-methylcycloheptylisopropyl, 3-methylcyclopentylisopropyl, 3-methylcyclohexylisopropyl, dicyclopropylmethyl, t-butylcyclopropylmethyl, t-butylcyclopentylmethyl, 2-isopropylcyclopentyl, 2-t-butylcyclopentyl, 2-isopropylcyclohexyl, 2-t-butylcyclopentyl, 2-isopropylcyclohexyl, 2-t-butylcyclohexyl, 2-t-amylcyclopentyl, t-amylcyclopropylmethyl, dicyclobutylmethyl, t-butylcyclobutylmethyl, 3-methylcycloheptylisopropyl, 2-methylcycloheptylisopropyl, 2-methylcyclohexylisopropyl, 2-methylcyclopentylisopropyl etc.; cycloalkenes, e.g., cyclopentenyl, cyclohexenyl, cycloheptenyl, etc.; alkyl-substituted cycloalkenes e.g., 1-methyl-3-cyclopentenyl 1-methyl-3-cyclohexenyl, 1-methyl-3-cycloheptenyl, 1-methyl-4-cycloheptenyl, 3-cyclopentenylisopropyl, 3-cyclohexenylisopropyl, 3-cycloheptenylisopropyl, 4-cycloheptenylisopropyl, 3-cyclopentenylmethyl, 3-cyclopentenylethyl, 3-cyclohexenylpropyl, 3-cyclohexenylethyl, 3-cycloheptenylpropyl, 3-cycloheptenylethyl, 4-cycloheptenylmethyl, 4-cycloheptenylethyl, 2-methyl-3-cyclohexenyl, 2-methyl-3-cyclopentenyl, 2-methyl-3-cycloheptenyl, 2-methyl-4-cycloheptenyl, 3-methyl-3-cyclohexenyl, 3-methyl-3-cyclopentenyl, 3-methyl-3-cycloheptenyl, 4-methyl-3-cycloheptenyl, 4-methyl-3-cyclohexenyl, 4-methyl-3-cyclopentenyl, 5-methyl-3-cyclopentenyl, 5-methyl-3-cyclohexenyl, 5-methyl-3-cycloheptenyl, 6-methyl-3-cyclohexenyl, 6-methyl-3-cycloheptenyl, 2-methyl-2-cyclopentenyl 2-methyl-2-cyclohexenyl, 2-methyl-2-cycloheptenyl, 2-methyl-2-cyclopentenyl, 3-methyl-2-cyclohexenyl, 3-methyl-2-cycloheptenyl, 1-methyl-2-cyclopentenyl, 1-methyl-2-cyclohexenyl, 1-methyl-2-cycloheptenyl, 5-methyl-2-cyclohexenyl, 4-methyl-2-cyclopentenyl, 4-methyl-2-cycloheptenyl, 5-methyl-2-cyclohexenyl, 5-methyl-2-cycloheptenyl, 6-methyl-2-cyclohexenyl, 6-methyl-2-cycloheptenyl, 7-methyl-2-cycloheptenyl, 2,3-dimethyl-2-cyclopentenyl, 2,3-dimethyl-2-cyclohexenyl, 2,4-dimethyl-2-cyclopentenyl, 2,4-dimethyl-2-cyclohexenyl, 2,5-dimethyl-2-cyclohexenyl, 2,5-dimethyl-2-cycloheptenyl, 2,6-dimethyl-2-cyclohexenyl, 2,6-dimethyl-3-cyclohexenyl, 2,5-dimethyl-3-cyclohexenyl, 2,5-dimethyl-2-cyclopentenyl, 2,4-dimethyl-3-cyclopentenyl, 2,4-dimethyl-3-cyclohexenyl, 3,3-dimethyl-3-cyclopentenyl, 3,3-dimethyl-3-cyclohexenyl, 3,4-dimethyl-3-cyclopentenyl, 3,4-dimethyl-3-cyclohexenyl, 4,5-dimethylcyclo-3-pentenyl, 4,5-dimethyl-3-cyclo-3-hexenyl, 5,5-dimethyl-3-cyclohexenyl, 5,5-dimethyl-3-cyclopentenyl, 5,5-dimethyl-3-cycloheptenyl, 6,6-dimethyl-3-cyclohexenyl, 1,2-dimethyl-3-cyclopentenyl, 1,2-dimethyl-3-cyclohexenyl, 1,3-dimethyl-3-cyclopentenyl, 1,3-dimethyl-3-cyclohexenyl, 1,3-dimethyl-3-cycloheptenyl, 1,4-dimethyl-3-cyclopentenyl, 1,4-dimethyl-3-cyclohexenyl, 1,4-dimethyl-3-cyclohexenyl, 1,5-dimethyl-3-cyclopentenyl, 1,5-dimethyl-3-cyclohexenyl, 1,5-dimethyl-3-cycloheptenyl, 2,2,6-trimethyl-3-cyclohexenyl, 2,2,5-trimethyl-3-cyclohexenyl, 2,5,5-trimethyl-3-cyclohexenyl, 2,5,5-trimethyl-3-cyclopentenyl, 2,7,7-trimethyl-3-cycloheptenyl, 2,7,7-trimethyl-4-cycloheptenyl, 2,2,7-trimethyl-3-cycloheptenyl, 2,2,7-trimethyl-4-cycloheptenyl, 2,3,6-trimethyl-3-cyclohexenyl, 2,3,7-trimethyl-3-cycloheptenyl, 2,3,5-trimethyl-3-cyclopentenyl, 2,2,6,6-tetramethyl-3-cyclohexenyl, 2,2,5,5-tetramethyl-3-cyclopentenyl, 2,2,7,7-tetramethyl-3-cycloheptenyl, 2,3,5,5 -tetramethyl-3-cyclopentenyl, 2,3,6,6-tetramethyl-3-cyclohexenyl, 2,3,7,7-tetramethyl-3-cycloheptenyl, 2,3,6 6-tetramethyl-3-cycloheptenyl, 2,3,5,5-tetramethyl-3-cyclohexenyl, 2,3,4,5-tetramethyl-3-cyclopentenyl, 2,3,4,5-tetramethyl-3-cyclohexenyl, (4-ethylcyclohex-3-enyl)isopropyl, (4-propylcyclohex-3-enyl)isopropyl, (4-methylcyclohex-3-enyl)ethyl, (3-methylcyclohex-3-enyl)isopropyl (4-ethylcyclopent-3-enyl)isopropyl, (4-propylcyclopent-3-enyl)isopropyl, (4-methylcyclopent-3-enyl)isopropyl, (4-methylcyclopent-3-enyl)ethyl, (3-methylcyclopent3-enyl)isopropyl, (2-methylcyclohex-3-enyl)isopropyl, (2-methylcyclopent-3-enyl)isopropyl, etc; bicyclic compounds, such as norbornyl, norcaranyl, norpinanyl, bicyclo [2.2.2] octyl, etc.; alkyl substituted bicyclic compounds, e.g., 6,6-dimethyl-bicyclo [3.1.1] heptyl, 6,7,7-trimethylnorbornyl (bornyl or camphanyl), pinanyl, thujanyl, caranyl,fenchyl, 2-norbornylmethyl, 2-norbornylethyl, 2-norbornylpropyl, 3-norbornylpropyl, etc.; unsubstituted and alkyl-substituted bicycloalkenes such as norborenyl, norpinenyl, norcarenyl, 2-(4-norborenyl)ethyl, pinenyl, carenyl, fenchenyl, etc.; and tricyclo compounds such as adamantyl and alkyl-substituted adamantyl, etc.

The preferred R₁ is cycloalkyl or bicycloalkyl or alkyl-substituted cycloalkyl or bicycloalkyl, especially where the alkyl group is in the β or β' positions. Further, preference exists for compounds in which R₁ is a cycloalkyl with two, three or four alkyl groups in the β, β' positions such as β,β,β',β'-tetraalkyl-substituted cyclopentyl, cyclobutyl, cyclohexyl and cycloheptyl, as well as β,β,β'-trialkyl substituted cyclobutyl, cyclopropyl, cyclohexyl, cyclopentyl, and cycloheptyl, and fenchyl. Also preferred are β-alkylcycloalkyls in which the alkyl group is isopropyl or tertiary butyl.

These novel compounds are effective sweetness agents when used alone or in combination with other sweeteners in an ingesta, e.g., foodstuffs or pharmaceuticals. For example, other natural and/or artificial sweeteners which may be used with the novel compounds of the present invention include sucrose, fructose, corn syrup solids, dextrose, xylitol, sorbitol, mannitol, acetosulfam, thaumatin, invert sugar, saccharin, thiophene saccharin, meta-aminobenzoic acid, metahydroxybenzoic acid, cyclamate, chlorosucrose, dihydrochalcone, hydrogenated glucose syrups, aspartame (L-aspartyl-L-phenylalanine methyl ester) and other dipeptides, glycyrrhizin and stevioside and the like. These sweeteners when employed with the sweetness agents of the present invention, it is believed, could produce synergistic sweetness responses.

Furthermore, when the sweetness agents of the present invention are added to ingesta, the sweetness agents may be added alone or with nontoxic carriers such as the abovementioned sweeteners or other food ingredients such as acidulants and natural and artificial gums. Typical foodstuffs, and pharmaceutical preparations, in which the sweetness agents of the present invention may be used are, for example, beverages including soft drinks, carbonated beverages, ready to mix beverages and the like, infused foods (e.g. vegetables or fruits), sauces, condiments, salad dressings, juices, syrups, desserts, including puddings, gelatin and frozen desserts, like ice creams, sherbets, icings and flavored frozen desserts on sticks, confections, toothpaste, mouthwash, chewing gum, cereals, baked goods, intermediate moisture foods (e.g. dog food) and the like.

In order to achieve the effects of the present invention, the compounds described herein are generally added to the food product at a level which is effective to perceive sweetness in the food stuff and suitably is in an amount in the range of from about 0.0005 to 2% by weight based on the consumed product. Greater amounts are operable but not practical. Preferred amounts are in the range of from about 0.001 to about 1% of the foodstuff. Generally, the sweetening effect provided by the present compounds are experienced over a wide pH range, e.g. 2 to 10 preferably 3 to 7 and in buffered and unbuffered formulations.

It is desired that when the sweetness agents of this invention are employed alone or in combination with another sweetner, the sweetener or combination of sweeteners provide a sucrose equivalent in the range of from about 2 weight percent to about 40 weight percent and more preferably from about 3 weight percent to about 15 weight percent in the foodstuff or pharmaceutical.

A taste procedure for determination of sweetness merely involves the determination of sucrose equivalency. Sucrose equivalence for sweeteners are readily determined. The amount of a sweetener that is equivalent to a given weight percent sucrose can be determined by having a panel of tasters taste solutions of a sweetener at known concentrations and match its sweetness to standard solutions of sucrose.

In order to prepare compounds of the present invention several reaction schemes may be employed. In one reaction scheme compounds of the general formula II (protected α-aminodicarboxylic acid) and III (etherified hydroxy amino compound) are condensed to form compounds of the general formula IV. Subsequent removal of protecting groups A and B from compounds of general formula IV give the desired compounds of general formula I. ##STR6##

In these, group A is an amino protecting group, B is a carboxyl protecting group and the remaining groups have the same meaning as previously described. A variety of protecting groups known in the art may be employed. Examples of many of these possible groups may be found in "Protective Groups in Organic Synthesis" by T. W. Green, John Wiley and Sons, 1981. Among the preferred groups that may be employed are benzyloxycarbonyl for A and benzyl for B. When A includes a free hydroxy group suitable protecting groups can be employed as known in the art.

Coupling of compounds with general formula II to compounds having general formula III employs established amide-forming techniques. One such technique uses dicyclohexylcarbodiimide (DCC) as the coupling agent. The DCC method may be employed with or without additives such as 4-dimethylaminopyridine or copper(II). The DCC coupling reaction generally proceeds at room temperature, however, it may be carried out from about -20° to 50° C. in variety of solvents inert to the reactants. Thus suitable solvents include, but are not limited to, N,N-dimethylformamide, methylene chloride, toluene and the like. Preferably the reaction is carried out under an inert atmosphere such as argon or nitrogen. Coupling usually is complete within 2 hours but may take as long as 24 hours depending on reactants.

Various other amide-forming methods can be employed to prepare the desired compounds using suitable derivatives of the free-carboxy group in compounds of structure II, e.g., acid halide, mixed anhydride with acetic acid and similar derivatives. The following illustrates such methods using aspartic acid as the amino dicarboxylic acid.

One such method utilizes the reaction of N-protected aspartic anhydrides with the selected amino compound of formula III. Thus compounds of formula III can be reacted directly in inert organic solvents with L-aspartic anhydride having its amino group protected by a formyl, carbobenzloxy, or p-methoxycarbobenzloxy group which is subsequently removed after coupling to give compounds of general formula I. The N-acyl-L-aspartic anhydrides are prepared by reacting the corresponding acids with acetic anhydride in amounts of 1.0-1.2 moles per mole of the N-acyl-L-aspartic acid at 0° to 60° C. in an inert solvent. The N-acyl-L-aspartic anhydrides are reacted with preferably 1 to 2 moles of compounds of formula III in an organic solvent capable of dissolving both and inert to the same. Representative solvents are ethyl acetate, methyl propionate, tetrahydrofuran, dioxane, ethyl ether, N,N-dimethylformamide and benzene. The reaction proceeds smoothly at 0° to 30° C. The N-acyl group is removed after coupling by catalytic hydrogenation with palladium on carbon or with HBr or HCl in a conventional manner. U.S. Pat. No. 3,879,372 discloses that this coupling method can also be performed in an aqueous solvent at a temperature of -10° to 50° C. and at a pH of 4-12.

Compounds of formula III are prepared by art-recognized procedures from known compounds or readily preparable intermediates. For example, the cycloalkanol can be reacted with the appropriate nitroalkene in an inert solvent. As in any organic reaction, solvents can be employed such as methylene chloride, ether, tetrahydrofuran, dioxane, chloroform and the like. The reaction is normally effected at 0° C., but temperatures ranging from -78° C. to 100° C. can be employed. Usually an inert atmosphere of nitrogen or argon is supplied. The nitro group of the formed product is then reduced by catalytic hydrogenation, e.g., H₂ /Pd or H₂ /Nickel.

Compound III can be prepared from the reaction of an cycloalkanol and the appropriate N-protected alkyl aziridine in an inert solvent. Inert solvents include methylene chloride, ether, tetrahydrofuran, dioxane, chloroform and the like. The reaction is normally effected at cold temperatures, e.g., 0° C. but temperatures ranging from -78° C. to -100° C. can be employed. Usually an inert atmosphere of nitrogen or argon is employed.

Compounds of general formula III may be synthesized from N-protected ethanolamine compounds by employing a variety of etherification methods known in the art. Some of these methods may be found in "Modern Synthetic Reactions", 2nd ed., by H. O. House, W. A. Benjamin, Inc., 1972; "Advanced Organic Chemistry", 2nd ed., by J. March McGraw-Hill, 1977, and "Compendium of Organic Synthetic Methods", Vol. 1 and 2, by I. T. Harrison and S. Harrison, Wiley-Interscience, 1971 and 1974.

One possible etherification method is the acid catalyzed reaction of N-protected ethanolamine compounds with an appropriate olefinic precursor of the desired Y moiety. For example when Y is R₁, N-carbobenzyloxy ethanolamine is reacted with methylenecyclopentane to obtain the N-protected intermediate of general formula III in which R₁ represents 1-methyl cyclopentane. This intermediate is then deprotected to give a compound of formula III having R₁ equal to 1-methylcyclopentane. When cycloalkadienes are used, the product is a cycloalkenyl ether. As illustrative examples, the following R₁ olefinic precursors can be utilized to give the corresponding R₁ group:

    ______________________________________                                         R.sub.1 Precursor  R.sub.1 Group                                               ______________________________________                                         methylenecyclobutane                                                                              1-methylcyclobutyl                                          1-methyl-1-cyclobutene                                                                            1-methylcyclobutyl                                          1-methyl-1-cyclopentene                                                                           1-methylcyclopentyl                                         1-methyl-1-cyclohexene                                                                            1-methylcyclohexyl                                          methylenecyclohexane                                                                              1-methylcyclohexyl                                          1,2-dimethyl-1-cyclohexene                                                                        1,2-dimethylcyclohexyl                                      1-methyl-1-cycloheptene                                                                           1-methylcycloheptyl                                         1-ethyl-1-cyclohexene                                                                             1-ethylcyclohexyl                                           1-ethyl-1-cyclopentene                                                                            1-ethylcyclopentyl                                          1,3-cyclopentadiene                                                                               2-cyclopentenyl                                             1-methyl-1,4-cyclohexadiene                                                                       1-methyl-1-cyclohex-3-enyl                                  d-limonene         1,1-dimethyl-1-(4'-methyl-                                                     cyclohex-3'-enyl)methyl                                     ______________________________________                                    

The reaction of an appropriate olefinic R₁ precursor with an N-protected ethanolamine compound is preferably carried out in the presence of an acid catalyst. Any acid is employable but a mineral acid such as sulfuric acrd is advantageous. Usually an excess of from 1.2 to 50 moles of the olefin precursor is utilized. Reaction temperatures are in the range of -10° to 40° C. and reaction times range from 2 to 48 hours. The reaction is carried out in a solvent that will dissolve both reactants and is inert to both as well. Solvents include, but are not limited to methylene chloride, toluene, tetrahydrofuran, chloroform and the like. Usually an inert atmosphere of nitrogen or argon is supplied.

Another possible etherification method is the base, or other catalyst, promoted reaction of N-protected ethanolamine compound with Y-X, where X is an organic leaving group such as halide, tosylate or mesylate. Any base normally employed to deprotonate an alcohol may be used, such as sodium hydride, sodium hydroxide, triethylamine, or diisopropyl ethylamine. Reaction temperatures are in the range of -78° to 100° C. and the reaction times vary from 2 to 48 hours. The reaction is carried out in a solvent that will dissolve both reactants and is inert to both as well. Solvents include, but are not limited to, diethyl ether, tetrahydrofurn, N,N-dimethylformamide, dimethylsulfoxide, and the like. Usually an inert atmosphere of nitrogen or argon is supplied.

Alternatively, a neutral catalyst such as mercury (II) salts or nickel (II) 2,4-pentanedionate may be employed in this reaction. These reactions are also carried out in inert solvents at room temperature or above. The intermediate formed in this reaction is deprotected to yield compounds of formula III.

A third method is the solvomercuration-demercuration reaction of the appropriate olefinic precursor of R₁ with an N-protected ethanolamine compound. This reaction is carried out in the presence of mercuric acetate or mercury trifluoroacetate at a reaction temperature of -10° to 100° C. in a solvent which will dissolve both reactants and is inert to both. Solvents include, but are not limited to, diethyl ether, tetrahydrofuran, methylene chloride, and the like. Reaction times vary from 5 minutes to 24 hours. The resulting organomercury intermediate is reduced in situ with basic aqueous sodium borohydride, or other reducing agents, to remove the mercury, followed by deprotection to yield compounds of general formula III.

A further method of etherification is the reaction of an N-protected compound of the formula

    NH.sub.2 --C(A)(A')--CH(R.sub.5)X

where X is halide, tosylate, mesylate or other leaving groups, with Y--OH using a base or other catalyst. Any base normally employed to deprotonate an alcohol may be used, including sodium hydride, sodium hydroxide, triethylamine, or diisopropyl ethylamine. The reaction may be run either with or without additives, for example, copper salts. Reaction temperatures are in the range of -78° C. to 100° C., and reaction times vary from 2 to 48 hours. The reaction is carried out in a solvent that will dissolve both reactants and is inert to both. Solvents include, but are not limited to, diethyl ether, tetrahydrofuran, N,N-dimethylformamide, dimethylsulfoxide, and the like. Usually an inert atmosphere of nitrogen or argon is supplied.

Alternatively, a neutral catalyst such as mercury (II) salts or nickel (II) 2,4-pentanedionate may be employed in this reaction. These are also carried out in inert solvents at room temperature or above. This product is then deprotected to yield compounds of general formula III.

With regard to the removal of protecting groups from compounds of formula IV and N-protected precursors of formula III, a number of deprotecting techniques are known in the art and can be utilized to advantage depending on the nature of the protecting groups. Among such techniques is catalytic hydrogenation utilizing palladium on carbon or transfer hydrogenation with 1,4-cyclohexadiene. Generally the reaction is carried at room temperature but may be conducted from 5° to 65° C. Usually the reaction is carried out in the presence of a suitable solvent which may include, but are not limited to water, methanol, ethanol, dioxane, tetrahydrofuran, acetic acid, t-butyl alcohol, isopropanol or mixtures thereof. The reaction is usually run at a positive hydrogen pressure of 50 psi but can be conducted over the range of 20 to 250 psi. Reactions are generally quantitative taking 1 to 24 hours for completion.

In any of the previous synthetic methods the desired products are preferably recovered from reaction mixtures by crystallization. Alternatively, normal or reverse-phase chromatography may be utilized as well as liquid/liquid extraction or other means.

The desired compounds of formula I are usually obtained in the free acid form; they may also be recovered as their physiologically acceptable salts, i.e., the corresponding amino salts such as hydrochloride, sulfate, hydrosulfate, nitrate, hydrobromide, hydroiodide, phosphate or hydrophosphate; or the alkali metal salts such as the sodium, potassium, lithium, or the alkaline earth metal salts such as calcium or magnesium, as well as aluminum, zinc and like salts.

Conversion of the present new compounds of formula I into their physiologically acceptable salts is carried out by conventional means, as for example, bringing the compounds of formula I into contact with a mineral acid, an alkali metal hydroxide, an alkali metal oxide or carbonate or an alkaline earth metal hydroxide, oxide, carbonate or other complexed form.

These physiologically acceptable salts can also be utilized as sweetness agents usually having increased solubility and stability over their free forms.

It is known to those skilled in the art that the compounds of the present invention having asymmetric carbon atoms may exist in racemic or optically active forms. All of these forms are contemplated within the scope of the invention.

The compounds of the present invention have one asymmetric site, which is designated by an asterik (*) in the formula below, and two pseudoasymmetric sites which are designated by a double asterik (**): ##STR7## Whenever A is identical to A' and R₄ is hydrogen, the compounds of the present invention have only one asymmetric site, designated by the asterik, in the dicarboxylic acid moiety. Although both the D and L forms are possible; the preferred compounds are those in which the dicarboxylic acid group is in the L-configuration. Whenever, the groups A' and A are different and R₄ is not hydrogen, the carbon atoms designated by the double asteriks become asymmetric centers and the compounds of the present invention will contain at least three asymmetric centers. If only A is different from A' or R₄ is not hydrogen, then the compounds of the present invention contain at least two asymmetric centers. Regardless, the configuration around each of the asymmetric sites, whenever present, may exist in either the D or L forms, and all possible stereoisomers are contemplated to be within the scope of the present invention. Since the aspartyl group is in the L-configuration, whenever an asymmetric center is present at either of the other two carbon sites, the compounds of the present invention are diastereomers, which can be separated, if desired, by art-recognized techniques, as, for example, chromatography. However, mixtures of at least any two stereoisomers exhibit sweetness properties and are useful as sweeteners.

The following examples further illustrate the invention.

EXAMPLE 1 N-(L-Aspartyl)-1-(2-aminopropoxy)-2,2,5,5-tetramethylcyclopentane

Method A:

2,2,5,5-Tetramethyl-1-cyclopentanol is added to a dry flask under argon at 0° C. Dry tetrahydrofuran is added with a syringe. Sodium hydride (60% dispersion in oil) is added quickly in one portion and the contents of the flask are stirred for one hour at room temperature. A 10 mM solution of 18-crown-6-ether in acetonitrile is added with a syringe and the flask cooled to 0° C. A tetrahydrofuran solution of 2-nitropropene is added with vigorous stirring over a 10 minute period. After completion of the reaction as judged by thin layer chromatography, it is quenched with saturated ammonium chloride and extracted with ethyl acetate. The organic layer is dried over MgSO₄ and evaporated to yield 1-(2-nitropropoxy)-2,2,5,5-tetramethylcyclopentane.

1-(2-Nitropropoxy)-2,2,5,5-tetramethylcyclopentane is dissolved in methanol and hydrogenated at 50 psi with Raney nickel T-1 as a catalyst. The reaction mixture is filtered through Celite and evaporated to yield 1-(2-aminopropoxy)-2,2,5,5-tetramethylcyclopentane.

Method B:

2-Methyl aziridine is dissolved in CH₂ Cl₂ and triethylamine under argon at 0° C. Benzylchloroformate is added and the contents of the flask are at room temperature overnight. The mixture is poured into 10% citric acid and is extracted with CHCl₃. The organic layer is washed with dilute aqueous NaHCO₃ and dried over MgSO₄. The solution is evaporated to yield N-Cbz-2-methyl aziridine.

N-Cbz-2-Methyl aziridine and 2,2,5,5-tetramethyl-1-cyclopentanol are dissolved in CH₂ Cl₂ at 0° C. under argon. Boron trifluoride etherate is added and the flask is stirred overnight. The contents are poured into saturated NaHCO₃ and are extracted with ethyl acetate. The organic layer is dried over MgSO₄ and evaporated to yield N-Cbz-1-(2-aminopropoxy)-2,2,5,5-tetramethylcyclopentane.

N-Cbz-1-(2-Aminopropoxy)-2,2,3,5-tetramethylcyclopentane is dissolved in CH₃ OH and hydrogenated over 5% Pd/C in a Parr hydrogenation apparatus. When the reaction is complete the mixture is filtered through Celite and concentrated to yield 1-(2-amino-propoxy)-2,2,5,5-tetramethylcyclopentane.

To a magnetically stirred solution of 1-(2-aminopropoxy)-2,2,5,5-tetramethylcyclopentane in dry dimethylformamide at 0° C. under argon atmosphere is added N-Cbz-L-aspartic acid beta-benzyl ester followed by copper (II) chloride and dicyclohexyl carbodiimide. This is stirred for 18 hours, after which the reaction mixture is poured into 0.1 N HCl and extracted with ethyl acetate. The organic phase is washed with saturated NaHCO₃ and then water, and dried over MgSO₄. Evaporation of the solvent yielded N-(N'-Cbz-L-aspartyl beta-benzyl ester)-1-(2-aminopropoxy)-2,2,5,5-tetramethylcyclopentane.

N-(N'-Cbz-L-aspartyl beta-benzyl ester)-1-(2-aminopropoxy)-2,2,5,5-tetramethylcyclopentane is dissolved in CH₃ OH and hydrogenated over 5% Pd/C in a Parr apparatus. Upon completion of the reaction the mixture is filtered and concentrated to yield N-(L-aspartyl)-1-(2-aminopropoxy)-2,2,5,5-tetramethylcyclopentane.

Similarly, by using the appropriate starting materials, the following compounds are also prepared:

N-(L-Aspartyl)-1-(2-aminopropoxy)-2,2,5-trimethylcyclopentane;

N-(L-Aspartyl)-1-(2-aminopropoxy)-2,5-dimethylcyclopentane;

N-(L-Aspartyl)-1-(2-aminopropoxy)-dicylopropylmethane;

N-(L-Aspartyl)-1-(2-aminopropoxy)-fenchane.

N-L-Aspartyl-1-(2-aminopropoxy)-1-t-butylcyclopropylmethane.

N-L-Aspartyl-1-(2-aminopropoxy)-1-isopropyl-1cyclopropylmethane.

N-L-Aspartyl-1-(2-aminopropyl)-2-t-butylcyclopentane.

EXAMPLE 2 N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane

Method A:

2,2,5,5-Tetramethyl-1-cyclopentanol is added to a dry flask under argon at 0° C. Dry tetrahydrofuran was added with a syringe. Sodium hydride (60% dispersion in oil) is added quickly in one portion and the contents of the flask are stirred for one hour at room temperature. A 10 mM solution of 18-crown-6-ether in acetonitrile is added with a syringe and the flask cooled to 0° C. A tetrahydrofuran solution of 2-nitropropene is added with vigorous stirring over a 10 minute period. After completion of the reaction, as judged by thin layer chromatography, it is quenched with dimethyl sulfate, poured into saturated ammonium chloride and extracted with ethyl acetate. The organic layer is dried over MgSO₄ and evaporated to yield 1-(2-nitro-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane.

1-(2-Nitro-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane is dissolved in methanol and hydrogenated at 50 psi with Raney nickel T-1 as a catalyst. The reaction mixture is filtered through Celite and evaporated to yield 1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane.

Method B:

2,2-Dimethyl aziridine is dissolved in CH₂ Cl₂ and triethylamine under argon at 0° C. Benzylchloroformate is added and the contents of the flask are stirred at room temperature overnight. The mixture is poured into 10% citric acid and extracted with CHCl₃. The organic layer is washed with dilute aqueous NaHCO₃ and dried over MgSO₄. The solution is evaporated to yield N-Cbz-2,2-dimethylaziridine.

N-Cbz-2,2-Dimethyl aziridine and 2,2,5,5-tetramethyl-1-cyclopentanol are dissolved in CH₂ Cl₂ at 0° C. under argon. Boron trifluoride etherate is added and the flask is stirred overnight. The contents are poured into saturated NaHCO₃ and extracted with ethyl acetate. The organic layer is dried over MgSO₄ and evaporated to yield N-Cbz-1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane.

N-Cbz-1-(2-amino-2-methylpropoxy)-2,2,5,5-cyclopentane is dissolved in CH₃ OH and hydrogenated over 5% Pd/C in a Parr hydrogenation apparatus. When the reaction is complete the mixture is filtered through Celite and concentrated to yield 1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane.

Method C:

2-Methyl-2-aminopropanol is dissolved in saturated aqueous NaHCO₃ at room temperature. Di-tert-butyldicarbonate is added in tert-butanol. The contents are stirred overnight and then extracted with ethyl acetate. The organic layer is dried over MgSO₄ and filtered. The filtrate is evaporated to give N-Boc-2-amino-2-methylpropanol.

N-Boc-2-Amino-2-methylpropanol is dissolved in triethylamine under argon at 0° C. Methanesulfonyl chloride is added and the mixture is stirred overnight. The solution is poured into 10% aqueous citric acid and extracted with ethyl acetate. The organic layer is dried over MgSO₄, filtered and evaporated to give N-Boc-2-amino-2-methyl-1-propyl mesylate.

2,2,5,5-Tetramethyl-1-cyclopentanol is added to a dry flask under argon at 0° C. Dry tetrahydrofuran is added with a syringe. Sodium hydride (60% dispersion in oil) is added quickly in one portion and the contents of the flask are stirred for one hour at room temperature. A 10 mM solution of 18-crown-6-ether in acetonitrile is added with a syringe and the flask cooled to 0° C. A tetrahydrofuran solution of N-Boc-2-amino-2-methyl-1-propyl mesylate is added with vigorous stirring over a 10 minute period. After completion of the reaction, as judged by thin layer chromatography, it is quenched with dimethyl sulfate, poured into saturated ammonium chloride and extracted with ethyl acetate. The organic layer is dried over MgSO₄ and evaporated to yield N-Boc-1-(2-amino-2-methylpropoxy)-tetramethyl 2,2,5,5-cyclopentane.

N-Boc-1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethyl cyclopentane is dissolved in trifluoroacetic acid and stirred overnight. The solution is poured into 0 water and neutralized with 20% aqueous KOH. The mixture is extracted with ethyl acetate, dried over MgSO₄, filtered and evaporated to give 1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane.

To a magnetically stirred solution of 1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane in dry dimethylformamide at 0° C. under argon atmosphere is added N-Cbz-L-aspartic acid beta-benzyl ester followed by copper (II) chloride and dicyclohexylcarbodiimide. This is stirred for 18 hours, after which the reaction mixture is poured into 0.1 N HCl and extracted with ethyl acetate. The organic phase is washed with saturated NaHCO₃ and then water, and dried over MgSO₄. Evaporation of the solvent yields N-(N'-Cbz-L-aspartyl beta-benzyl ester)-1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane.

N-(N'-Cbz-L-aspartyl beta-benzyl ester)-1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane is dissolved in CH₃ OH and hydrogenated over 5% Pd/C in a Parr apparatus. Upon completion of the reaction the mixture is filtered and concentrated to yield N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-2,2,5,5-tetramethylcyclopentane

Similarly, by using the appropriate starting materials, the following compounds are also prepared:

N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-2,2,5-trimethylcyclopentane.

N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-2,5-dimethylcyclopentane.

N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-dicyclopropylmethane.

N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-fenchane.

N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-1-t-butylcyclopropylmethane.

N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-1-isopropyl-1-cyclopropylmethane.

N-(L-Aspartyl)-1-(2-amino-2-methylpropoxy)-2-t-butylcyclopentane.

EXAMPLE 3 1-(N-(Aspartyl)amino)-1-[(2,2,5,5-tetramethylcyclopentoxy) methyl]cyclopropane

To a suspension of 1-amino-1-cyclopropane carboxylic acid in dry diethyl ether under argon at 0° C. is slowly added 1 M borane in tetrahydrofuran with vigorous stirring. The contents are stirred overnight and then water is added dropwise to destroy the remainder of the borane. The mixture is acidified with 2 N HCl and then brought to approximately pH 11 with 20% KOH and saturated with NaCl. The product is extracted with ethyl acetate and the organic layer dried over MgSO₄. Filtration and evaporation of the solvent yields 1-amino-1-hydroxymethylcyclopropane.

1-Amino-1-hydroxymethylcyclopropane is dissolved in saturated aqueous NaHCO₃ at room temperature. Di-tert-butyldicarbonate is added in tert-butanol. The contents are stirred overnight and then extracted with ethyl acetate. The organic layer is dried over MgSO₄ and filtered. The filtrate is evaporated to give N-Boc-1-amino-1-hydroxymethylcyclopropane.

N-Boc-1-amino-1-hydroxymethylcyclopropane is dissolved in triethylamine under argon at 0° C. Methanesulfonyl chloride is added with a syringe and the contents stirred at room temperature overnight. The solution is poured into 10% aqueous citric acid and extracted with ethyl acetate. The organic layer is dried over MgSO₄ filtered and evaporated to give N-Boc-1-amino-1-hydroxymethylcyclopropane mesylate.

2,2,5,5-Tetramethyl-1-cyclopentanol is added to a dry flask under argon at 0° C. Dry tetrahydrofuran is added with a syringe. Sodium hydride (60% dispersion in oil) is added quickly in one portion and the contents of the flask are stirred for one hour at room temperature. A 10 mM solution of 18-crown-6- ether in acetonitrile is added with a syringe and the flask cooled to 0° C. A tetrahydrofuran solution of N-Boc-1-amino-1-hydroxymethylcyclopropane mesylate is added with vigorous stirring over a 10 minute period. After completion of the reaction, as judged by thin layer chromatography, it is quenched with dimethyl sulfate, poured into saturated ammonium chloride and extracted with ethyl acetate. The organic layer is dried over MgSO₄ and evaporated to yield N-Boc-O-(2,2,5,5-tetramethyl-1-cyclopentyl)-1-amino-1-hydroxymethylcyclopropane.

N-Boc-O-(2,2,5,5-tetramethyl-1-cyclopentyl)-1-amino-1-hydroxymethylcyclopropane is dissolved in trifluoroacetic acid and stirred overnight. The solution is poured into water and neutralized with 20% aqueous KOH. The mixture is extracted with ethyl acetate, dried over MgSO₄, filtered and evaporated to give O-(2,2,5,5-tetramethyl-1-cyclopentyl)-1-amino-1-hydroxymethylcyclopropane.

To a magnetically stirred solution of O-(2,2,5,5-tetramethyl-1-cyclopentyl)-1-amino-1-hydroxymethylcyclopropane in dry dimethylformamide at 0° C. under argon atmosphere is added N-Cbz-L-aspartyl acid beta-benzyl ester followed by copper (II) chloride and dicyclohexylcarbodiimide. This is stirred for 18 hours after which the reaction mixture is poured into 0.1 N HCl and extracted with ethyl acetate. The organic phase is washed with saturated NaHCO₃ and then water, and dried over MgSO₄. Evaporation of the solvent yields N-(N'-Cbz-L-aspartyl beta-benzyl ester)-O-(2,2,5,5-tetramethyl-1-cyclopentyl)-1-amino-1-hydroxymethylcyclopropane.

N-(N'-Cbz-L-Aspartyl beta-benzyl ester)- O-(2,2,5,5-tetramethyl-1-cyclopentyl)-1-amino-1-hydroxymethylcyclopropane is dissolved in CH₃ OH and hydrogenated over 5% Pd/C in a Parr apparatus. Upon completion of the reaction the mixture is filtered and concentrated to yield N-(L-aspartyl)-O-(2,2,5,5-tetramethyl-1-cyclopentyl)-1-amino-1-hydroxymethylcyclopropane.

Similarly, by using the appropriate cycloalkanol, the following compounds are also prepared:

1-(N-(L-Aspartyl)amino)-1-[(2,2,5-trimethylcyclopentoxy)methyl]cyclopropane;

1-(N-(L-Aspartyl)amino)-1-[(2,5-dimethylcyclopentoxy)methyl]cyclopropane;

1-(N-(L-Aspartyl)amino)-1-(dicyclopropylmethoxymethyl)cyclopropane;

1-(N-(L-Aspartyl)amino)-1-(fenchoxymethyl)cyclopropane.

1-(N-(L-Aspartyl)amino)-1-[(2-t-butylcyclopentoxymethyl)]cyclopropane.

1-(N-(L-Aspartyl)amino)-1-[(1-t-butyl-1-cyclopropylmethyl)oxymethyl]cyclopropane.

1-(N-(L-Aspartyl)amino)-1-[(1-isopropyl-1-cyclopropylmethyl)oxymethyl]cyclopropane.

EXAMPLE 4 N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-2,2,5,5-tetramethyl cyclopropane A. L-N-Triphenylmethyl serine methyl ester

A solution of L-serine methyl ester hydrochloride (100 g), triphenylmethylchloride (179.3 g) and triethylamine (197 ml) is stirred at 0° C. for 2 hours, then allowed to warm to room temperature overnight. The solution is then washed successively with 10% aqueous citric acid and water, dried over magnesium sulfate, and the solvent evaporated to yield the product.

B. L-1-Triphenylmethyl-aziridine-2-carboxylic acid methyl ester

A mixture of compound A (212 g), methanesulfonyl chloride (45.6 ml), and pyridine (1.76 l) is stirred at 0° C., then allowed to warm slowly to room temperature overnight. Ethyl acetate (1.5 l) is added, and the resulting solution washed with 10% aqueous citric acid and water, dried over magnesium sulfate and the solvent removed. The residual oil is dissolved in tetrahydrofuran (2.5 l) and triethylamine (143 ml) is added. The mixture is heated at reflux overnight, then cooled and most of the solvent is removed under vacuum. The residual oil is dissolved in ethyl acetate (2 l) and the solution is washed successively with 10% aqueous citric acid, saturated aqueous sodium bicarbonate, and water, and then dried over magnesium sulfate, after which the solvent is evaporated under vacuum. The residue is dissolved in hot methanol and the product crystallizes on cooling.

C. L-1-Benzyloxycarbonylaziridine-2-carboxylic acid methyl ester

To a cold solution (0° C.) of compound B (17.0 g) and methanol (100 ml) in dichloromethane (100 ml) is added concentrated sulfuric acid (5.0 ml). The mixture is stirred at 0° C. for 10 min. Approximately half of the solvent is removed under vacuum, and the residue is dissolved in ether. This is made basic with sodium bicarbonate and extracted with dichloromethane (3×25 ml). To these combined extracts is added triethylamine (4.63 g) and the solution is cooled to 0° C. Benzyl chloroformate (7.80 g), is added, and the mixture is allowed to warm to room temperature overnight. The solution is then washed successively with 1M aqueous hydrochloric acid and saturated aqueous sodium bicarbonate, dried over magnesium sulfate, and the solvent is removed under vacuum to yield a brown oil (7.0 g). The product is purified by column chromatography on silica gel (4:1 hexanes: ethyl acetate, eluent) to yield compound C.

D. N-Benzyloxycarbonyl-O-2,2,5,5-tetramethylcyclopentyl-L-serine methyl ester

To a solution of compound C (1.00 g) and 2,2,5,5-tetramethylcyclopentanol (1.2 g) in dichloromethane (20 ml) is added boron trifluoride diethyl etherate (15 drops). The mixture is stirred at room temperature for 4 hours, then washed with water, dried over magnesium sulfate and the solvent is evaporated. The residue is purified by column chromatography (silica gel, 10:1, hexanes: ethyl acetate, eluent) to yield compound D.

E. O-2,2,5,5-Tetramethylcyclopentyl-L-serine methyl ester

The product of D is dissolved in methanol in a Parr hydrogenation bottle and purged with argon. Palladium on carbon (5%) is added and hydrogenation carried out at 50 psi. After cessation of hydrogen uptake, the contents of the bottle are filtered through celite and evaporated to give the product.

F. N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-2,2,5,5-tetramethyl cyclopentane

The product of E is dissolved in ether and is reduced with LiAlH₄ to give 1-(2-amino-3-hydroxypropoxy)-2,2,5,5-tetramethyl cyclopentane. To a magnetically stirred solution of this product in dry dimethyl formamide at 0° C. under argon atmosphere is added N-CbZ-L-aspartic acid-beta-benzyl ester, followed by Copper (II) chloride and dicyclohexylcarbodiimide. This is stirred for 18 hours, after which the reaction mixture is poured into 0.1 N HCl and extracted with ethyl acetate. The organic phase is washed with saturated NaHCO₃ and then water and is dried over MgSO₄. The solvents evaporated off to give N-(N'-Cb₂ -L-aspartyl-beta benzyl ester)-1-(2-amino-3-hydroxypropoxy)-2,2,5,5-tetramethylcyclopentane.

This product is dissolved in CH₃ OH and hydrogenated over 5% Pd/C in a Parr apparatus. Nipon completion of the reaction, the mixture is filtered and concentrated to yield the final product.

Similarly, by utilizing the above procedure, and the appropriate cycloalkanol, the following compounds are also synthesized:

N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-2,2,5-trimethylcyclopentane;

N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-2,5-dimethylcyclopentane;

N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-dicyclopropylmethane;

N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-fenchane;

N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-2-t-butylcyclopentane;

N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-1-t-butyl-1-cyclopropylmethane;

N-(L-Aspartyl)-1-(2-amino-3-hydroxypropoxy)-1-isopropyl-1-cyclopropylmethane.

EXAMPLE 5 N-(L-Aspartyl)-1-(2-amino-3-methoxypropoxy)-2,2,5,5-tetramethylcyclopentane

To a suspension of N-Benzyloxycarbonyl-O-2,2,5,5-tetramethylcyclopentyl-L-serine methyl ester (prepared as in Example 4) in dry diethyl ether under argon at 0° C. is slowly added 1 M borane in tetrahydrofuran with vigorous stirring. The contents are stirred overnight and then water is added dropwise to destroy the remainder of the borane. The mixture is acidified with 2N HCl and then brought to approximately pH 11 with 20% KOH and saturated with NaCl. The product is extracted with ethyl acetate and the organic layer dried over MgSO₄ and filtered and the solvent is evaporated off.

The product of the preceding paragraph is dissolved in methylene chloride and methylated with dimethylsulfate to afford the 1-(2-N-CbZ-amino-3-hydroxypropoxy)-2,2,5,5-tetramethylcyclopentane. This product is dissolved in methanol in a Parr hydrogenation bottle and purged with argon. Palladium on carbon (5%) is added and hydrogenation carried out at 50 psi. After cessation of hydrogen uptake, the contents of the bottle are filtered through celite and evaporated to give 1-(2-amino-3-methoxypropoxy)-2,2,5,5-tetramethylcyclopentane.

To a magnetically stirred solution of this product in dry dimethyl formamide at 0° C. under argon atmosphere is added N-CbZ-L-aspartic acid beta-benzyl ester followed by copper (II) chloride and dicyclohexyl carbodiimide. This is stirred for 18 hours, after which the reaction mixture is poured into 0.1N HCl and extracted with ethyl acetate. The organic phase is washed with saturated NaHCO₃, and then water and dried over the MgSO₄. The solvent is evaporated off to give N-(N-CbZ-L-aspartyl-beta benzyl ester)-1-(2-amino-3-methoxypropoxy)-2,2,5,5-tetramethylcyclopentane.

This product is dissolved in CH₃ OH and hydrogenated over 5% Pd/C in a Parr apparatus. Upon completion of the reaction, the mixture is filtered and concentrated to yield the final product.

Similarly, by utilizing the above procedure, and the appropriate cycloalkanol, the following compounds are also synthesized:

N-(L-Aspartyl)-1-(2-amino-3-methoxypropoxy)-2,2,5-trimethylcyclopentane;

N-(L-Aspartyl)-1-(2-amino-3-methoxypropoxy)-2,5-dimethylcyclopentane;

N-(L-Aspartyl)-1-(2-amino-3-methoxypropoxy)dicyclopropylmethane;

N-(L-Aspartyl)-1-(2-amino-3-methoxypropoxy)fenchane;

N-(L-Aspartyl)-1-(2-amino-3-methoxypropoxy)-2-t-butylcyclopentane;

N-(L-Aspartyl)-1-(2-amino-3-methoxypropoxy)-1-t-butyl-1-cyclopropylmethane;

N-(L-Aspartyl)-1-(2-amino-3-methoxypropoxy)-1-isopropyl-1-cyclopropylmethane. 

What is claimed is:
 1. A compound represented by the formula: ##STR8## wherein A is hydrogen, alkyl containing 1-3 carbon atoms, hydroxyalkyl containing 1-3 carbon atoms or alkoxymethyl wherein the alkoxy contains 1-3 carbon atoms;A' is hydrogen or alkyl containing 1-3 carbon atoms; alternatively A and A' taken together with the carbon atom to which they are attached form cycloalkyl containing 3-4 carbon atoms; Y is --(CHR₂)_(n) --R₁ or --CHR₃ R₄ ; R₁ is cycloalkyl, cycloalkenyl, lower alkyl substituted cycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl or tricycloalkyl containing up to 10 ring carbon atoms and up to a total of 12 carbon atoms; R₂ and R₅ are each H or alkyl containing 1-4 carbon atoms; R₃ and R₄ are each cycloalkyl containing 3-4 ring carbon atoms; n=0 or 1; and m=0 or 1; and food-acceptable salts thereof.
 2. A compound according to claim 1 wherein R₁ is cyclopentyl or cyclohexyl containing a total of up to 10 carbon atoms.
 3. A compound according to claim 2 wherein n=0.
 4. A compound according to claim 1 wherein R₁ is mono-, di-, tri- or tetramethyl cycloalkyl or bicycloalkyl containing up to 10 carbon atoms.
 5. A compound according to claim 4 wherein R₁ is a β-methyl-substituted cycloalkyl or bicycloalkyl.
 6. A compound according to claim 4 wherein R₁ is a β,β or β,β'-dimethyl-substituted cycloalkyl or bicycloalkyl.
 7. A compound according to claim 4 wherein R₁ is a β,β,β'-trimethyl-substituted cycloalkyl or bicycloalkyl.
 8. A compound according to claim 4 wherein R₁ is a β,β,β',β'-tetramethyl-substituted cycloalkyl or bicycloalkyl.
 9. A compound according to claim 1 wherein R₃ and R₄ are cyclopropyl.
 10. A compound represented by the formula: ##STR9## wherein A and A' are each hydrogen or alkyl containing 1-3 carbon atoms;Y is --(CHR₂)_(n) --R₁ or --CHR₃ R₄ ; R₁ is cycloalkyl, cycloalkenyl, lower alkyl substituted cycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl or tricycloalkyl containing up to 10 ring carbon atoms and up to a total of 12 carbon atoms; R₂ is H or alkyl containing 1-4 carbon atoms; R₃ and R₄ are each cycloalkyl containing 3-4 ring carbon atoms; n=0 or 1; and m=0 or 1; and food-acceptable salts thereof.
 11. A compound according to claim 10 wherein R₁ is cyclopentyl or cyclohexyl containing a total of up to 10 carbon atoms.
 12. A compound according to claim 11 wherein n=0.
 13. A compound according to claim 10 wherein R₁ is mono-, di-, tri or tetramethyl cycloalkyl or bicycloalkyl containing up to 10 carbon atoms.
 14. A compound according to claim 13 wherein R₁ is a β-methyl-substituted cycloalkyl or bicycloalkyl.
 15. A compound according to claim 13 wherein R₁ is a β,β or β,β'-dimethyl-substituted cycloalkyl or bicycloalkyl.
 16. A compound according to claim 13 wherein R₁ is a β,β,β'-trimethyl-substituted cycloalkyl or bicycloalkyl.
 17. A compound according to claim 13 wherein R₁ is a β,β,β',β'-tetramethyl-substituted cycloalkyl or bicycloalkyl.
 18. A compound according to claim 10 wherein R₃ and R₄ are cyclopropyl.
 19. A compound represented by the formula: ##STR10## wherein A is hydroxyalkyl containing 1-3 carbon atoms;A' is hydrogen or alkyl containing 1-3 carbon atoms; Y is --(CHR₂)_(n) --R₁ or --CHR₃ R₄ ; R₁ is cycloalkyl, cycloalkenyl, lower alkyl substituted cycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl or tricycloalkyl containing up to 10 ring carbon atoms and up to a total of 12 carbon atoms; R₂ is H or alkyl containing 1-4 carbon atoms; R₃ and R₄ are each cycloalkyl containing 3-4 ring carbon atoms; n=0 or 1; m=0 or 1; and food-acceptable salts thereof.
 20. A compound according to claim 19 wherein R₁ is cyclopentyl or cyclohexyl containing a total of up to 10 carbon atoms.
 21. A compound according to claim 20 wherein n=0.
 22. A compound according to claim 19 wherein R₁ is mono-, di-, tri or tetramethyl cycloalkyl or bicycloalkyl containing up to 10 carbon atoms.
 23. A compound according to claim 22 wherein R₁ is a β-methyl-substituted cycloalkyl or bicycloalkyl.
 24. A compound according to claim 22 wherein R₁ is a β,β or β,β'-dimethyl-substituted cycloalkyl or bicycloalkyl.
 25. A compound according to claim 22 wherein R₁ is a β,ββ'-trimethyl-substituted cycloalkyl or bicycloalkyl.
 26. A compound according to claim 22 wherein R₁ is a β,β,β',β'-tetramethyl-substituted cycloalkyl or bicycloalkyl.
 27. A compound according to claim 19 wherein R₃ and R₄ are cyclopropyl.
 28. A compound represented by the formula: ##STR11## wherein A is alkoxymethyl wherein the alkoxy contains 1-3 carbon atoms;A' is hydrogen or alkyl containing 1-3 carbon atoms; Y is --(CHR₂)_(n) --R₁ or --CHR₃ R₄ ; R₁ is cycloalkyl, cycloalkenyl, lower alkyl substituted cycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl or tricycloalkyl containing up to 10 ring carbon atoms and up to a total of 12 carbon atoms; R₂ is H or alkyl containing 1-4 carbon atoms; R₃ and R₄ are each cycloalkyl containing 3-4 ring carbon atoms; n=0, 1 or 2; and m=0 or 1; and food-acceptable salts thereof.
 29. A compound according to claim 28 wherein R₁ is cyclopentyl or cyclohexyl containing a total of up to 10 carbon atoms.
 30. A compound according to claim 29 wherein n=0.
 31. A compound according to claim 28 wherein R₁ is mono-, di-, tri or tetramethyl cycloalkyl or bicycloalkyl containing up to 10 carbon atoms.
 32. A compound according to claim 31 wherein R₁ is a β-methyl-substituted cycloalkyl or bicycloalkyl.
 33. A compound according to claim 31 wherein R₁ is a β,β or β,β'-dimethyl-substituted cycloalkyl or bicycloalkyl.
 34. A compound according to claim 31 wherein R₁ is a β,β,β'-trimethyl-substituted cycloalkyl or bicycloalkyl.
 35. A compound according to claim 31 wherein R₁ is a β,β,β', β'-tetramethyl-substituted cycloalkyl or bicycloalkyl.
 36. A compound according to claim 28 wherein R₃ and R₄ are cyclopropyl.
 37. A compound represented by the formula: ##STR12## wherein A and A' taken together with the carbon atom to which they are attached form cycloalkyl containing 3-4 carbon atoms;Y is --(CHR₂)_(n) --R₁ or --CHR₃ R₄ ; R₁ is cycloalkyl, cycloalkenyl, lower alkyl substituted cycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl or tricycloalkyl containing up to 10 ring carbon atoms and up to a total of 12 carbon atoms; R₂ is H or alkyl containing 1-4 carbon atoms; R₃ and R₄ are each cycloalkyl containing 3-5 ring carbon atoms; n=0 or 1; and m=0 or 1; and food-acceptable salts thereof.
 38. A compound according to claim 37 wherein R₁ is cyclopentyl or cyclohexyl containing a total of up to 10 carbon atoms.
 39. A compound according to claim 38 wherein n=0.
 40. A compound according to claim 37 wherein R₁ is mono-, di-, tri- or tetramethyl cycloalkyl or bicycloalkyl containing up to 10 carbon atoms.
 41. A compound according to claim 40 wherein R₁ is a β-methyl-substituted cycloalkyl or bicycloalkyl.
 42. A compound according to claim 40 wherein R₁ is a β,β or β,β'-dimethyl-substituted cycloalkyl or bicycloalkyl.
 43. A compound according to claim 40 wherein R₁ is a β,β,β'-trimethyl-substituted cycloalkyl or bicycloalkyl.
 44. A compound according to claim 40 wherein R₁ is a β,β,β',β'-tetramethyl-substituted cycloalkyl or bicycloalkyl.
 45. A compound according to claim 37 wherein R₃ and R₄ are cyclopropyl.
 46. A compound of the formula: ##STR13## wherein A is hydrogen, alkyl containing 1-3 carbon atoms, hydroxyalkyl containing 1-3 carbon atoms or alkoxymethyl wherein the alkoxy contains 1-3 carbon atoms;A' is hydrogen or alkyl containing 1-3 carbon atoms; alternatively A and A' taken together with the carbon atom to which they are attached form cycloalkyl containing 3-4 carbon atoms; Y is --R₁ or --CHR₃ R₄ ; R₁ is cycloalkyl, cycloalkenyl, lower alkyl substituted cycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl or tricycloalkyl containing up to 10 ring carbon atoms and up to a total of 12 carbon atoms; and R₃ and R₄ are each cycloalkyl containing 3-4 carbon atoms; and m is 0 or 1; and food acceptable salts thereof.
 47. A compound according to claim 46 wherein R₁ is cyclopentyl or cyclohexyl containing a total of up to 10 carbon atoms.
 48. A compound according to claim 46 wherein R₁ is mono-, di-, tri- or tetramethyl cycloalkyl or bicycloalkyl containing up to 10 carbon atoms.
 49. A compound according to claim 47 wherein R₁ is a β-methyl-substituted cycloalkyl or bicycloalkyl.
 50. A compound according to claim 47 wherein R₁ is a β,β'-dimethyl-substituted cycloalkyl or bicycloalkyl.
 51. A compound according to claim 47 wherein R₁ is a β,β,β'-trimethyl-substituted cycloalkyl or bicycloalkyl.
 52. A compound according to claim 47 wherein R₁ is a β,β,β',β'-tetramethyl-substituted cycloalkyl or bicycloalkyl.
 53. A compound according to claim 46 wherein R₃ and R₄ are cyclopropyl.
 54. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminopropoxy)-2,2,5,5-tetramethylcyclopentane.
 55. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminopropoxy)-2,2,5-trimethylcyclopentane.
 56. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminopropoxy)-2,5-dimethylcyclopentane.
 57. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminopropoxy)-dicyclopropylmethane.
 58. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminopropoxy)-fenchane.
 59. The compound according to claim 19 which is N-(L-aspartyl)-1-(2-amino-3-hydroxypropoxy)-2,2,5,5-tetramethylcyclopentane.
 60. The compound according to claim 19 which is N-(L-aspartyl)-1-(2-amino-3-hydroxypropoxy)-2,2,5-trimethylcyclopentane.
 61. The compound according to claim 19 which is N-(L-aspartyl)-1-(2-amino-3-hydroxypropoxy)-2,5-dimethylcyclopentane.
 62. The compound according to claim 19 which is N-(L-aspartyl)-1-(2-amino-3-hydroxypropoxy)-dicyclopropylmethane.
 63. The compound according to claim 19 which is N-(L-aspartyl)-1-(2-amino-3-hydroxypropoxy)-fenchane.
 64. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminoethoxy)-2,2,5,5-tetramethylcyclopentane.
 65. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminoethoxy)-2,2,5-trimethylcyclopentane.
 66. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminoethoxy)-2,5-dimethylcyclopentane.
 67. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminoethoxy)-dicyclopropylmethane.
 68. The compound according to claim 10 which is N-(L-aspartyl)-1-(2-aminoethoxy)-fenchane.
 69. The compound according to claim 37 which is 1-N-(L-aspartyl)amino)-1-[(2,2,5,5-tetramethylcyclopentyloxy)methyl]-cyclopropane.
 70. The compound according to claim 37 which is 1-N-(L-aspartyl)amino)-1-[(2,2,5-trimethylcyclopentyloxy) methyl]cyclopropane.
 71. The compound according to claim 37 which is 1-N-(L-aspartyl)amino)-1-[(2,5-dimethylcyclopentyloxy)methyl]cyclopropane.
 72. The compound according to claim 37 which is 1-N-(L-aspartyl)amino)-1-(dicyclopropylmethyloxymethyl)cyclopropane.
 73. The compound according to claim 37 which is 1-N-(L-aspartyl)amino)-1-fenchyloxymethyl)cyclopropane.
 74. The compound according to claim 28 which is N-(L-aspartyl)-1-(2-amino-3-methoxypropoxy)-2,2,5,5-tetramethylcyclopentane.
 75. The compound according to claim 28 which is N-(L-aspartyl)-1-(2-amino-3-methoxypropoxy)-2,2,5-trimethylcyclopentane.
 76. The compound according to claim 28 which is N-(L-aspartyl)-1-(2-amino-3-methoxypropoxy)-2,5-dimethylcyclopentane.
 77. The compound according to claim 28 which is N-(L-aspartyl)-1-(2-amino-3-methoxypropoxy)-dicyclopropylmethane.
 78. The compound according to claim 28 which is N-(L-aspartyl)-1-(2-amino-3-methoxypropoxy)-fenchane.
 79. The compound according to claim 28 which is N-(L-aspartyl)-1-(2-amino-3-methoxypropoxy)-2-t-butylcyclopentane.
 80. The compound according to claim 28 which is N-(L-aspartyl)-1-(2-amino-3-methoxypropoxy)-1-t-butyl-1-cyclopropylmethane.
 81. The compound according to claim 28 which is N-(L-aspartyl)-1-(2-amino-3-methoxypropoxy)-1-isopropyl-1-cyclopropylmethane.
 82. The compound according to claim 37 which is 1-(N-L-aspartyl)amino)-1-[(2-t-butylcyclopentyl)oxymethyl]cyclopropane.
 83. The compound according to claim 37 which is 1-(N-L-aspartyl)amino)-1-(1-t-butyl-1-cyclopropylmethoxymethyl)-cyclopropane.
 84. The compound according to claim 37 which is 1- (N-L-aspartyl)amino)-1-(1-isopropyl-1-cyclopropylmethoxymethyl)-cyclopropane.
 85. The compound according to claim 10 which is N-L-aspartyl-1-(2-aminoethoxy)-2-t-butylcyclopentane.
 86. The compound according to claim 10 which is N-L-aspartyl-1-(2-aminoethoxy)-1-t-butyl-1-cyclopropylmethane.
 87. The compound according to claim 10 which is N-L-aspartyl-1-(2-aminoethoxy)-1-isopropyl-1-cyclopropylmethane.
 88. The compound according to claim 19 which is N-(L-aspartyl)-1-(2-amino-3-hydroxypropoxy)-2-t-butylcyclopentane.
 89. The compound according to claim 19 which is N-(L-aspartyl)-1-(2-amino-3-hydroxypropoxy)-1-t-butyl-1-cyclopropylmethane.
 90. The compound according to claim 19 which is N-(L-aspartyl)-1-(2-amino-3-hydroxypropoxy)-1-isopropyl-1-cyclopropylmethane. 